Recirculating ball screw assembly

Abstract

Ball screws are described that may be incorporated into other devices such as a pulley assembly or a differential device. The ball screws include a threaded shaft defining a central longitudinal axis with a threaded nut threadedly coupled thereto to define at least one track in between them. Each track forms a continuous loop around an infield protrusion and is filled with a plurality of rolling elements filling. Each rolling element has the same radius from the central longitudinal axis such that the nut can rotate at higher speeds without the rolling elements locking up as a result of centripetal force.

What is claimed is: 
     
       1. A ball screw comprising:
 a unitary threaded shaft defining a central longitudinal axis; 
 a threaded nut threadedly coupled to the threaded shaft to define at least one track located within the unitary threaded shaft, each track forming a continuous loop around an infield protrusion that defines a first end partition defining a first turnaround and a second end partition defining a second turnaround, the continuous loop defining a leading path and a trailing path, the trailing path having a trailing width including a fixed width that is greater than a leading width of the leading path, and the trailing width and the leading width both being measured from the infield protrusion; 
 a plurality of rolling elements filling each track, the rolling elements configured to circulate from the trailing path back to the leading path of the track during operation of the ball screw; 
 wherein each rolling element located in both the leading path and the trailing path of the continuous loop have a same radius from the central longitudinal axis. 
 
     
     
       2. The ball screw of  claim 1  wherein an exterior surface of the nut is connectable to a first rotatable member for rotation therewith. 
     
     
       3. The ball screw of  claim 2  wherein the nut rotates at speeds of about 2,000 to about 20,000 rpm. 
     
     
       4. The ball screw of  claim 2  wherein the unitary threaded shaft is connectable to a second rotatable member to be driven by the first rotatable member. 
     
     
       5. The ball screw of  claim 2  wherein the unitary threaded shaft is connectable to a second rotatable member for rotation therewith; wherein no translation of the nut occurs when the unitary threaded shaft and the nut have the same rotational speed and translation of the nut occurs when either the unitary threaded shaft or the nut rotates at a speed different relative to the other. 
     
     
       6. The ball screw of  claim 1  wherein the threaded nut has a double start or a triple start threading. 
     
     
       7. The ball screw of  claim 1  wherein the roller elements are spherical, uniformly cylindrical, or tapered cylindrical bearings. 
     
     
       8. The ball screw of  claim 1  wherein the leading path is from the first end partition to the second end partition and the trailing path is from the second end partition to the first end partition; wherein the trailing path circulates the roller elements unloaded back to the leading path. 
     
     
       9. The ball screw of  claim 1  wherein the infield protrusion and the first and second end partitions protrude from an exterior surface of the unitary threaded shaft. 
     
     
       10. The ball screw of  claim 1  wherein the threaded nut includes less than a full turn, a full turn, or multiple turns. 
     
     
       11. The ball screw of  claim 1  wherein the nut is coupled to a pulley body for rotation therewith. 
     
     
       12. The ball screw of  claim 11  wherein the unitary threaded shaft is coupled to a drive plate connectable to a clutch mechanism. 
     
     
       13. A pulley assembly comprising:
 a pulley body having a bore; 
 a hub defining an axis of rotation disposed within the bore of the pulley body; 
 a ball screw disposed about the hub, the ball screw capable of axial expansion when the pulley body rotates in a predominant direction and comprising: 
 a unitary threaded shaft translatable along the hub; 
 a threaded nut threadedly coupled to the threaded shaft to define at least one track located within the unitary threaded shaft and coupled to the pulley body for rotation therewith, each track forming a continuous loop around an infield protrusion that defines a first end partition defining a first turnaround and a second end partition defining a second turnaround, the continuous loop defining a leading path and a trailing path, the trailing path having a trailing width including a fixed width that is greater than a leading width of the leading path, and the trailing width and the leading width both being measured from the infield protrusion; 
 a plurality of rolling elements filling each track, the rolling elements configured to circulate from the trailing path back to the leading path of the track during operation of the ball screw; 
 wherein each rolling element located in both the leading path and the trailing path of the continuous loop have a same radius from the axis of rotation; and 
 a clutch mechanism disposed about the hub, the clutch mechanism being activatable into an engaged position by the axial expansion of the ball screw; 
 wherein in the engaged position the axial expansion of the ball screw activates the clutch mechanism, which links the pulley body to the hub for simultaneous rotation in the predominant direction. 
 
     
     
       14. The pulley assembly of  claim 13  wherein the threaded nut has a double start threading or a triple start threading, and the roller elements are spherical, uniformly cylindrical, or tapered cylindrical bearings. 
     
     
       15. The pulley assembly of  claim 13  wherein the leading path is from the first end partition to the second end partition and the trailing path is from the second end partition to the first end partition; wherein the trailing path circulates the roller elements unloaded back to the leading path. 
     
     
       16. The pulley assembly of  claim 13  wherein the infield protrusion protrudes from an exterior surface of the unitary threaded shaft. 
     
     
       17. The pulley assembly of  claim 13  further comprising a biasing member biasing the nut or shaft of the ball screw axially into maintained contact during operation of the pulley assembly, the biasing member disposed between the ball screw and a cap or between the ball screw and the clutch mechanism. 
     
     
       18. The pulley assembly of  claim 17  wherein the biasing member includes one or more Belleville washers. 
     
     
       19. The pulley assembly of  claim 13  wherein the clutch mechanism includes a clutch pack or a cone clutch. 
     
     
       20. The pulley assembly of  claim 13  wherein when the pulley body rotates in a direction opposite the predominant direction or experiences a deceleration, the clutch mechanism disengages from the ball screw and allows the hub to rotate independently of the pulley body in the predominant direction under its own momentum.